Makeup of the U.S. Senate at the start of this Congress, color-coded by party. Note: The orange stripes in New York and the gray stripes in Virginia denote ConservativeJames Buckley and Independent Harry Byrd, respectively.

Senators are popularly elected statewide every two years, with one-third beginning new six-year terms with each Congress. Preceding the names in the list below are Senate class numbers, which indicate the cycle of their election. In this Congress, Class 1 means their term began in the last Congress, requiring reelection in 1976; Class 2 means their term began with this Congress, requiring reelection in 1978; and Class 3 means their term ended with this Congress, requiring reelection in 1974.

Nick Begich (D) and Hale Boggs (D) were lost in a plane crash, and the estate of Rep. Begich was issued a presumptive death certificate from the State of Alaska during previous congress. Both were also declared dead pursuant to H. R. Res. 1 issued January 3, 1973.

^Joe Moakley (D-MA) was elected as "Independent Conservative," based on official report of Congress by Benjamin Guthrie. “Statistics of the Presidential and Congressional Election of November 7, 1972.” But he was sworn in as a Democrat at the beginning of the Congress, January 3, 1973. [1]

Martis, Kenneth C. (1989). The Historical Atlas of Political Parties in the United States Congress. New York: Macmillan Publishing Company.